Nautical glass
The nautical glass (plural: glass) is a nautical unit of time. It corresponds to half an hour and is used to organize the watch duty at sea.
The name goes back to the hourglass made of glass that was used to measure the time units for the watch. After each hourglass, which was calibrated for half an hour, a bell was struck, which is also known as "glass".
Larger periods of time can be specified relatively or absolutely (based on a 4-hour wake cycle) in glasses, e.g. B. "4 glasses later" corresponds to "after 2 hours" or "by 5 glasses", which is 2:30, 6:30, 10:30, 14:30, 18:30 or 22:30 depending on the waking cycle corresponds.
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Wiktionary: Glass - explanations of meanings, word origins, synonyms, translations